In the continuous casting of steel slabs, ingots, billets or blooms, a tundish on a casting floor is aligned with an upright mold into which the molten metal is fed. Upon solidification of at least a peripheral portion of the ingot, the latter moves continuously from the mold and is generally guided in a curved path from its upright original orientation to a horizontal orientation at which the slab may meet a reheating furnace, a sizing mill, a cutoff device severing individual lengths from the continuous strand, etc.
Along this curved path the slab is supported and guided by rollers as it cools, the rollers being assembled in clusters or racks successively encountered by the strand. Such racks are generally termed support and guide racks and may be associated with water spray nozzles, lattices or networks.
It is common practice to provide so-called multibranch casting lines which comprise a plurality of molds in transversely spaced relationship which can be fed by a common ladle with molten steel, for example, through respective tundishes or through a single tundish provided with a number of outlets, or by a tundish which is movable selectively into alignment with each mold. Each mold is then associated with respective group of curved support and guide racks of the type described.
For a discussion of the principles involved in continuous casting and details of the elements described, reference is made to pages 708 ff. of The Making, Shaping and Treating of Steel, United States Steel, Co. Pittsburgh, PA, 1971.
When the rollers, spray manifolds, nozzles or other elements of these racks become soiled or contaminated, in the event of a breakdown in the continuous casting operation, and when a change in the nature or shape of the casting to be produced is to be effected, it is desirable to remove these racks and replace them with other racks in as rapid and efficient a manner as is possible to minimize the downtime of the unit.
It is conventional to make these racks so that they can be moved as a unit with remnants of a casting therein and/or of the open-door type so that they can be withdrawn from position leaving the casting remnant in place, or to make them movable so that replacement of the racks is facilitated.
In general, the ingot mold is first removed by the portal or roof crane of the steel-making plant, albeit with considerable difficulty because of the tightness of space and the fact that continuous casting lines are usually close to one another and associated with auxiliary equipment such that access to the mold is difficult. Thereafter, the racks below the mold are removed by special cranes mounted below the casting floor. The casting floor is the level in the plant at which the tundish is located and below which the curved racks are arranged.
In the removal of supporting guide racks of the aforedescribed type in conventional installations, moreover, the racks must be drawn through special openings provided in the casting floor in a time-consuming dismounting process which interrupts the output of the plant for considerable periods.
To eliminate these extensive downtimes, special carriages have been proposed enabling insertion and withdrawal of the racks and which can be displaced in the opposite direction from the casting direction.
However, in some continuous casting installations and especially in multibranch casting installations, the tundish can be mounted on a turntable which has a support or foundation behind the array of curved racks and thus prevents the use of this system for installing and removing the racks. Earlier systems which attempted to withdraw the racks from one side or the other have been ineffective because the presence of adjacent racks in multibranch casting lines has limited the possibility of movement in these directions. Increasing the spacing between the casting lines might enable such lateral techniques to be used effectively at the cost of much space in the mill.
Finally, mention must be made of efforts to extract and insert the racks in the direction of movement of the casting. In practice these systems have been found to be applicable only to single-line and double-line continuous casting installations. Otherwise, the additional lines interfered with the carriages which have been proposed for this purpose.